1. Field of the Invention
The invention proceeds from a combined current and voltage transformer for a metal-enclosed, gas-insulated high-voltage switching station, having a current sensor and a voltage sensor and a signal processing unit connected following the current and voltage sensor, in which the current sensor contains a coil wound in the shape of a torus and the voltage sensor contains a hollow cylindrical test electrode, and in which after installation in the metal enclosure the coil and test electrode concentrically surround a conductor of the switching station.
2. Discussion of Background
In this case, the invention refers to a prior art such as follows, for example, from DE-Al-2,325,441. A measuring transducer represented in FIG. 1 of this patent publication and intended for installation in a metal-enclosed, gas-insulated switching station contains a metal tube, fastened in an electrically insulated fashion to a mounting lug, as well as current transformer coils having mounted secondary windings. The metal tube and the current transformer coils supported by it and having the mounted secondary windings are arranged coaxially with a conductor of the switching station in the interior of the metal enclosure. The metal tube forms with the conductor the upper voltage capacitor of a capacitive divider at whose output a signal is present which corresponds to the voltage applied at the conductor. Signals which correspond to the current flowing in the conductor can be tapped at the secondary windings. The current transformer cores have large dimensions and contain, moreover, predominantly specifically heavy, ferromagnetic material. Consequently, the combined current and voltage transformer according to the prior art not only demands a lot of space, but because of its high weight requires a particularly sturdy and stable construction. In order to achieve good measurement accuracy, the capacitive divider requires, moreover, a lower voltage capacitor that is thermally stable.